New project, added one video file, one seqcuence, nothing on the timeline. When playing a video file in the source pannel, the video plays fine for two seconds, then it becomes jumpy, showing ONLY one frame every second or so. Imposible to do any work!! Even on playback resolution set at minimum allowed at 1/4

This is a new installation, version 6.0.3, running on Windows 8 on a core i5 @ 1.70 MHZ with intel HD Graphics 4000. Max cpu usage is 30% and memory available is more than half.

Your laptop is a very slow dual core machine, way underpowered for such material, whether it is a de facto standard or not. And it further hampered by the Intel Graphics. IMO you have two choices, either accept the slowness, or get a new machine.

Even a laptop with an i7 quad core at 2.2 GHZ and a GT 640M video card is around 21 times slower than a fast machine. Your CPU is 30% slower, has only half the cores, lacks a GT 640M card, so you can imagine is will be around 70 - 80 times slower and you are disappointed that your GoPro material can not be handled fluidly? GoPro is so demanding that it even gets the fastest system on its knees. Only in your case it is unbearable. I understand that, but here the blame can not be put on Adobe, it goes to GoPro for their extremely complex codec and not informing their clients that if you want to edit their material, you NEED a superfast and powerful computer and on yourself for getting such a very weak laptop, without considering the complexity of the codec you want to use.

The only way to make it partly workable with your laptop is converting to a more friendly format, but that may mean you run out of disk space.